Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * auth-scram.c
4 : * Server-side implementation of the SASL SCRAM-SHA-256 mechanism.
5 : *
6 : * See the following RFCs for more details:
7 : * - RFC 5802: https://tools.ietf.org/html/rfc5802
8 : * - RFC 5803: https://tools.ietf.org/html/rfc5803
9 : * - RFC 7677: https://tools.ietf.org/html/rfc7677
10 : *
11 : * Here are some differences:
12 : *
13 : * - Username from the authentication exchange is not used. The client
14 : * should send an empty string as the username.
15 : *
16 : * - If the password isn't valid UTF-8, or contains characters prohibited
17 : * by the SASLprep profile, we skip the SASLprep pre-processing and use
18 : * the raw bytes in calculating the hash.
19 : *
20 : * - If channel binding is used, the channel binding type is always
21 : * "tls-server-end-point". The spec says the default is "tls-unique"
22 : * (RFC 5802, section 6.1. Default Channel Binding), but there are some
23 : * problems with that. Firstly, not all SSL libraries provide an API to
24 : * get the TLS Finished message, required to use "tls-unique". Secondly,
25 : * "tls-unique" is not specified for TLS v1.3, and as of this writing,
26 : * it's not clear if there will be a replacement. We could support both
27 : * "tls-server-end-point" and "tls-unique", but for our use case,
28 : * "tls-unique" doesn't really have any advantages. The main advantage
29 : * of "tls-unique" would be that it works even if the server doesn't
30 : * have a certificate, but PostgreSQL requires a server certificate
31 : * whenever SSL is used, anyway.
32 : *
33 : *
34 : * The password stored in pg_authid consists of the iteration count, salt,
35 : * StoredKey and ServerKey.
36 : *
37 : * SASLprep usage
38 : * --------------
39 : *
40 : * One notable difference to the SCRAM specification is that while the
41 : * specification dictates that the password is in UTF-8, and prohibits
42 : * certain characters, we are more lenient. If the password isn't a valid
43 : * UTF-8 string, or contains prohibited characters, the raw bytes are used
44 : * to calculate the hash instead, without SASLprep processing. This is
45 : * because PostgreSQL supports other encodings too, and the encoding being
46 : * used during authentication is undefined (client_encoding isn't set until
47 : * after authentication). In effect, we try to interpret the password as
48 : * UTF-8 and apply SASLprep processing, but if it looks invalid, we assume
49 : * that it's in some other encoding.
50 : *
51 : * In the worst case, we misinterpret a password that's in a different
52 : * encoding as being Unicode, because it happens to consists entirely of
53 : * valid UTF-8 bytes, and we apply Unicode normalization to it. As long
54 : * as we do that consistently, that will not lead to failed logins.
55 : * Fortunately, the UTF-8 byte sequences that are ignored by SASLprep
56 : * don't correspond to any commonly used characters in any of the other
57 : * supported encodings, so it should not lead to any significant loss in
58 : * entropy, even if the normalization is incorrectly applied to a
59 : * non-UTF-8 password.
60 : *
61 : * Error handling
62 : * --------------
63 : *
64 : * Don't reveal user information to an unauthenticated client. We don't
65 : * want an attacker to be able to probe whether a particular username is
66 : * valid. In SCRAM, the server has to read the salt and iteration count
67 : * from the user's stored secret, and send it to the client. To avoid
68 : * revealing whether a user exists, when the client tries to authenticate
69 : * with a username that doesn't exist, or doesn't have a valid SCRAM
70 : * secret in pg_authid, we create a fake salt and iteration count
71 : * on-the-fly, and proceed with the authentication with that. In the end,
72 : * we'll reject the attempt, as if an incorrect password was given. When
73 : * we are performing a "mock" authentication, the 'doomed' flag in
74 : * scram_state is set.
75 : *
76 : * In the error messages, avoid printing strings from the client, unless
77 : * you check that they are pure ASCII. We don't want an unauthenticated
78 : * attacker to be able to spam the logs with characters that are not valid
79 : * to the encoding being used, whatever that is. We cannot avoid that in
80 : * general, after logging in, but let's do what we can here.
81 : *
82 : *
83 : * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
84 : * Portions Copyright (c) 1994, Regents of the University of California
85 : *
86 : * src/backend/libpq/auth-scram.c
87 : *
88 : *-------------------------------------------------------------------------
89 : */
90 : #include "postgres.h"
91 :
92 : #include <unistd.h>
93 :
94 : #include "access/xlog.h"
95 : #include "catalog/pg_authid.h"
96 : #include "catalog/pg_control.h"
97 : #include "common/base64.h"
98 : #include "common/hmac.h"
99 : #include "common/saslprep.h"
100 : #include "common/scram-common.h"
101 : #include "common/sha2.h"
102 : #include "libpq/auth.h"
103 : #include "libpq/crypt.h"
104 : #include "libpq/sasl.h"
105 : #include "libpq/scram.h"
106 : #include "miscadmin.h"
107 : #include "utils/builtins.h"
108 : #include "utils/timestamp.h"
109 :
110 : static void scram_get_mechanisms(Port *port, StringInfo buf);
111 : static void *scram_init(Port *port, const char *selected_mech,
112 : const char *shadow_pass);
113 : static int scram_exchange(void *opaq, const char *input, int inputlen,
114 : char **output, int *outputlen,
115 : const char **logdetail);
116 :
117 : /* Mechanism declaration */
118 : const pg_be_sasl_mech pg_be_scram_mech = {
119 : scram_get_mechanisms,
120 : scram_init,
121 : scram_exchange
122 : };
123 :
124 : /*
125 : * Status data for a SCRAM authentication exchange. This should be kept
126 : * internal to this file.
127 : */
128 : typedef enum
129 : {
130 : SCRAM_AUTH_INIT,
131 : SCRAM_AUTH_SALT_SENT,
132 : SCRAM_AUTH_FINISHED
133 : } scram_state_enum;
134 :
135 : typedef struct
136 : {
137 : scram_state_enum state;
138 :
139 : const char *username; /* username from startup packet */
140 :
141 : Port *port;
142 : bool channel_binding_in_use;
143 :
144 : /* State data depending on the hash type */
145 : pg_cryptohash_type hash_type;
146 : int key_length;
147 :
148 : int iterations;
149 : char *salt; /* base64-encoded */
150 : uint8 StoredKey[SCRAM_MAX_KEY_LEN];
151 : uint8 ServerKey[SCRAM_MAX_KEY_LEN];
152 :
153 : /* Fields of the first message from client */
154 : char cbind_flag;
155 : char *client_first_message_bare;
156 : char *client_username;
157 : char *client_nonce;
158 :
159 : /* Fields from the last message from client */
160 : char *client_final_message_without_proof;
161 : char *client_final_nonce;
162 : char ClientProof[SCRAM_MAX_KEY_LEN];
163 :
164 : /* Fields generated in the server */
165 : char *server_first_message;
166 : char *server_nonce;
167 :
168 : /*
169 : * If something goes wrong during the authentication, or we are performing
170 : * a "mock" authentication (see comments at top of file), the 'doomed'
171 : * flag is set. A reason for the failure, for the server log, is put in
172 : * 'logdetail'.
173 : */
174 : bool doomed;
175 : char *logdetail;
176 : } scram_state;
177 :
178 : static void read_client_first_message(scram_state *state, const char *input);
179 : static void read_client_final_message(scram_state *state, const char *input);
180 : static char *build_server_first_message(scram_state *state);
181 : static char *build_server_final_message(scram_state *state);
182 : static bool verify_client_proof(scram_state *state);
183 : static bool verify_final_nonce(scram_state *state);
184 : static void mock_scram_secret(const char *username, pg_cryptohash_type *hash_type,
185 : int *iterations, int *key_length, char **salt,
186 : uint8 *stored_key, uint8 *server_key);
187 : static bool is_scram_printable(char *p);
188 : static char *sanitize_char(char c);
189 : static char *sanitize_str(const char *s);
190 : static char *scram_mock_salt(const char *username,
191 : pg_cryptohash_type hash_type,
192 : int key_length);
193 :
194 : /*
195 : * The number of iterations to use when generating new secrets.
196 : */
197 : int scram_sha_256_iterations = SCRAM_SHA_256_DEFAULT_ITERATIONS;
198 :
199 : /*
200 : * Get a list of SASL mechanisms that this module supports.
201 : *
202 : * For the convenience of building the FE/BE packet that lists the
203 : * mechanisms, the names are appended to the given StringInfo buffer,
204 : * separated by '\0' bytes.
205 : */
206 : static void
207 76 : scram_get_mechanisms(Port *port, StringInfo buf)
208 : {
209 : /*
210 : * Advertise the mechanisms in decreasing order of importance. So the
211 : * channel-binding variants go first, if they are supported. Channel
212 : * binding is only supported with SSL, and only if the SSL implementation
213 : * has a function to get the certificate's hash.
214 : */
215 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
216 76 : if (port->ssl_in_use)
217 : {
218 12 : appendStringInfoString(buf, SCRAM_SHA_256_PLUS_NAME);
219 12 : appendStringInfoChar(buf, '\0');
220 : }
221 : #endif
222 76 : appendStringInfoString(buf, SCRAM_SHA_256_NAME);
223 76 : appendStringInfoChar(buf, '\0');
224 76 : }
225 :
226 : /*
227 : * Initialize a new SCRAM authentication exchange status tracker. This
228 : * needs to be called before doing any exchange. It will be filled later
229 : * after the beginning of the exchange with authentication information.
230 : *
231 : * 'selected_mech' identifies the SASL mechanism that the client selected.
232 : * It should be one of the mechanisms that we support, as returned by
233 : * scram_get_mechanisms().
234 : *
235 : * 'shadow_pass' is the role's stored secret, from pg_authid.rolpassword.
236 : * The username was provided by the client in the startup message, and is
237 : * available in port->user_name. If 'shadow_pass' is NULL, we still perform
238 : * an authentication exchange, but it will fail, as if an incorrect password
239 : * was given.
240 : */
241 : static void *
242 64 : scram_init(Port *port, const char *selected_mech, const char *shadow_pass)
243 : {
244 : scram_state *state;
245 : bool got_secret;
246 :
247 64 : state = (scram_state *) palloc0(sizeof(scram_state));
248 64 : state->port = port;
249 64 : state->state = SCRAM_AUTH_INIT;
250 :
251 : /*
252 : * Parse the selected mechanism.
253 : *
254 : * Note that if we don't support channel binding, either because the SSL
255 : * implementation doesn't support it or we're not using SSL at all, we
256 : * would not have advertised the PLUS variant in the first place. If the
257 : * client nevertheless tries to select it, it's a protocol violation like
258 : * selecting any other SASL mechanism we don't support.
259 : */
260 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
261 64 : if (strcmp(selected_mech, SCRAM_SHA_256_PLUS_NAME) == 0 && port->ssl_in_use)
262 8 : state->channel_binding_in_use = true;
263 : else
264 : #endif
265 56 : if (strcmp(selected_mech, SCRAM_SHA_256_NAME) == 0)
266 56 : state->channel_binding_in_use = false;
267 : else
268 0 : ereport(ERROR,
269 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
270 : errmsg("client selected an invalid SASL authentication mechanism")));
271 :
272 : /*
273 : * Parse the stored secret.
274 : */
275 64 : if (shadow_pass)
276 : {
277 64 : int password_type = get_password_type(shadow_pass);
278 :
279 64 : if (password_type == PASSWORD_TYPE_SCRAM_SHA_256)
280 : {
281 62 : if (parse_scram_secret(shadow_pass, &state->iterations,
282 : &state->hash_type, &state->key_length,
283 : &state->salt,
284 62 : state->StoredKey,
285 62 : state->ServerKey))
286 62 : got_secret = true;
287 : else
288 : {
289 : /*
290 : * The password looked like a SCRAM secret, but could not be
291 : * parsed.
292 : */
293 0 : ereport(LOG,
294 : (errmsg("invalid SCRAM secret for user \"%s\"",
295 : state->port->user_name)));
296 0 : got_secret = false;
297 : }
298 : }
299 : else
300 : {
301 : /*
302 : * The user doesn't have SCRAM secret. (You cannot do SCRAM
303 : * authentication with an MD5 hash.)
304 : */
305 4 : state->logdetail = psprintf(_("User \"%s\" does not have a valid SCRAM secret."),
306 2 : state->port->user_name);
307 2 : got_secret = false;
308 : }
309 : }
310 : else
311 : {
312 : /*
313 : * The caller requested us to perform a dummy authentication. This is
314 : * considered normal, since the caller requested it, so don't set log
315 : * detail.
316 : */
317 0 : got_secret = false;
318 : }
319 :
320 : /*
321 : * If the user did not have a valid SCRAM secret, we still go through the
322 : * motions with a mock one, and fail as if the client supplied an
323 : * incorrect password. This is to avoid revealing information to an
324 : * attacker.
325 : */
326 64 : if (!got_secret)
327 : {
328 2 : mock_scram_secret(state->port->user_name, &state->hash_type,
329 : &state->iterations, &state->key_length,
330 : &state->salt,
331 2 : state->StoredKey, state->ServerKey);
332 2 : state->doomed = true;
333 : }
334 :
335 64 : return state;
336 : }
337 :
338 : /*
339 : * Continue a SCRAM authentication exchange.
340 : *
341 : * 'input' is the SCRAM payload sent by the client. On the first call,
342 : * 'input' contains the "Initial Client Response" that the client sent as
343 : * part of the SASLInitialResponse message, or NULL if no Initial Client
344 : * Response was given. (The SASL specification distinguishes between an
345 : * empty response and non-existing one.) On subsequent calls, 'input'
346 : * cannot be NULL. For convenience in this function, the caller must
347 : * ensure that there is a null terminator at input[inputlen].
348 : *
349 : * The next message to send to client is saved in 'output', for a length
350 : * of 'outputlen'. In the case of an error, optionally store a palloc'd
351 : * string at *logdetail that will be sent to the postmaster log (but not
352 : * the client).
353 : */
354 : static int
355 128 : scram_exchange(void *opaq, const char *input, int inputlen,
356 : char **output, int *outputlen, const char **logdetail)
357 : {
358 128 : scram_state *state = (scram_state *) opaq;
359 : int result;
360 :
361 128 : *output = NULL;
362 :
363 : /*
364 : * If the client didn't include an "Initial Client Response" in the
365 : * SASLInitialResponse message, send an empty challenge, to which the
366 : * client will respond with the same data that usually comes in the
367 : * Initial Client Response.
368 : */
369 128 : if (input == NULL)
370 : {
371 : Assert(state->state == SCRAM_AUTH_INIT);
372 :
373 0 : *output = pstrdup("");
374 0 : *outputlen = 0;
375 0 : return PG_SASL_EXCHANGE_CONTINUE;
376 : }
377 :
378 : /*
379 : * Check that the input length agrees with the string length of the input.
380 : * We can ignore inputlen after this.
381 : */
382 128 : if (inputlen == 0)
383 0 : ereport(ERROR,
384 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
385 : errmsg("malformed SCRAM message"),
386 : errdetail("The message is empty.")));
387 128 : if (inputlen != strlen(input))
388 0 : ereport(ERROR,
389 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
390 : errmsg("malformed SCRAM message"),
391 : errdetail("Message length does not match input length.")));
392 :
393 128 : switch (state->state)
394 : {
395 64 : case SCRAM_AUTH_INIT:
396 :
397 : /*
398 : * Initialization phase. Receive the first message from client
399 : * and be sure that it parsed correctly. Then send the challenge
400 : * to the client.
401 : */
402 64 : read_client_first_message(state, input);
403 :
404 : /* prepare message to send challenge */
405 64 : *output = build_server_first_message(state);
406 :
407 64 : state->state = SCRAM_AUTH_SALT_SENT;
408 64 : result = PG_SASL_EXCHANGE_CONTINUE;
409 64 : break;
410 :
411 64 : case SCRAM_AUTH_SALT_SENT:
412 :
413 : /*
414 : * Final phase for the server. Receive the response to the
415 : * challenge previously sent, verify, and let the client know that
416 : * everything went well (or not).
417 : */
418 64 : read_client_final_message(state, input);
419 :
420 64 : if (!verify_final_nonce(state))
421 0 : ereport(ERROR,
422 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
423 : errmsg("invalid SCRAM response"),
424 : errdetail("Nonce does not match.")));
425 :
426 : /*
427 : * Now check the final nonce and the client proof.
428 : *
429 : * If we performed a "mock" authentication that we knew would fail
430 : * from the get go, this is where we fail.
431 : *
432 : * The SCRAM specification includes an error code,
433 : * "invalid-proof", for authentication failure, but it also allows
434 : * erroring out in an application-specific way. We choose to do
435 : * the latter, so that the error message for invalid password is
436 : * the same for all authentication methods. The caller will call
437 : * ereport(), when we return PG_SASL_EXCHANGE_FAILURE with no
438 : * output.
439 : *
440 : * NB: the order of these checks is intentional. We calculate the
441 : * client proof even in a mock authentication, even though it's
442 : * bound to fail, to thwart timing attacks to determine if a role
443 : * with the given name exists or not.
444 : */
445 64 : if (!verify_client_proof(state) || state->doomed)
446 : {
447 10 : result = PG_SASL_EXCHANGE_FAILURE;
448 10 : break;
449 : }
450 :
451 : /* Build final message for client */
452 54 : *output = build_server_final_message(state);
453 :
454 : /* Success! */
455 54 : result = PG_SASL_EXCHANGE_SUCCESS;
456 54 : state->state = SCRAM_AUTH_FINISHED;
457 54 : break;
458 :
459 0 : default:
460 0 : elog(ERROR, "invalid SCRAM exchange state");
461 : result = PG_SASL_EXCHANGE_FAILURE;
462 : }
463 :
464 128 : if (result == PG_SASL_EXCHANGE_FAILURE && state->logdetail && logdetail)
465 2 : *logdetail = state->logdetail;
466 :
467 128 : if (*output)
468 118 : *outputlen = strlen(*output);
469 :
470 128 : return result;
471 : }
472 :
473 : /*
474 : * Construct a SCRAM secret, for storing in pg_authid.rolpassword.
475 : *
476 : * The result is palloc'd, so caller is responsible for freeing it.
477 : */
478 : char *
479 90 : pg_be_scram_build_secret(const char *password)
480 : {
481 : char *prep_password;
482 : pg_saslprep_rc rc;
483 : char saltbuf[SCRAM_DEFAULT_SALT_LEN];
484 : char *result;
485 90 : const char *errstr = NULL;
486 :
487 : /*
488 : * Normalize the password with SASLprep. If that doesn't work, because
489 : * the password isn't valid UTF-8 or contains prohibited characters, just
490 : * proceed with the original password. (See comments at top of file.)
491 : */
492 90 : rc = pg_saslprep(password, &prep_password);
493 90 : if (rc == SASLPREP_SUCCESS)
494 88 : password = (const char *) prep_password;
495 :
496 : /* Generate random salt */
497 90 : if (!pg_strong_random(saltbuf, SCRAM_DEFAULT_SALT_LEN))
498 0 : ereport(ERROR,
499 : (errcode(ERRCODE_INTERNAL_ERROR),
500 : errmsg("could not generate random salt")));
501 :
502 90 : result = scram_build_secret(PG_SHA256, SCRAM_SHA_256_KEY_LEN,
503 : saltbuf, SCRAM_DEFAULT_SALT_LEN,
504 : scram_sha_256_iterations, password,
505 : &errstr);
506 :
507 90 : if (prep_password)
508 88 : pfree(prep_password);
509 :
510 90 : return result;
511 : }
512 :
513 : /*
514 : * Verify a plaintext password against a SCRAM secret. This is used when
515 : * performing plaintext password authentication for a user that has a SCRAM
516 : * secret stored in pg_authid.
517 : */
518 : bool
519 30 : scram_verify_plain_password(const char *username, const char *password,
520 : const char *secret)
521 : {
522 : char *encoded_salt;
523 : char *salt;
524 : int saltlen;
525 : int iterations;
526 30 : int key_length = 0;
527 : pg_cryptohash_type hash_type;
528 : uint8 salted_password[SCRAM_MAX_KEY_LEN];
529 : uint8 stored_key[SCRAM_MAX_KEY_LEN];
530 : uint8 server_key[SCRAM_MAX_KEY_LEN];
531 : uint8 computed_key[SCRAM_MAX_KEY_LEN];
532 : char *prep_password;
533 : pg_saslprep_rc rc;
534 30 : const char *errstr = NULL;
535 :
536 30 : if (!parse_scram_secret(secret, &iterations, &hash_type, &key_length,
537 : &encoded_salt, stored_key, server_key))
538 : {
539 : /*
540 : * The password looked like a SCRAM secret, but could not be parsed.
541 : */
542 0 : ereport(LOG,
543 : (errmsg("invalid SCRAM secret for user \"%s\"", username)));
544 0 : return false;
545 : }
546 :
547 30 : saltlen = pg_b64_dec_len(strlen(encoded_salt));
548 30 : salt = palloc(saltlen);
549 30 : saltlen = pg_b64_decode(encoded_salt, strlen(encoded_salt), salt,
550 : saltlen);
551 30 : if (saltlen < 0)
552 : {
553 0 : ereport(LOG,
554 : (errmsg("invalid SCRAM secret for user \"%s\"", username)));
555 0 : return false;
556 : }
557 :
558 : /* Normalize the password */
559 30 : rc = pg_saslprep(password, &prep_password);
560 30 : if (rc == SASLPREP_SUCCESS)
561 30 : password = prep_password;
562 :
563 : /* Compute Server Key based on the user-supplied plaintext password */
564 30 : if (scram_SaltedPassword(password, hash_type, key_length,
565 : salt, saltlen, iterations,
566 30 : salted_password, &errstr) < 0 ||
567 30 : scram_ServerKey(salted_password, hash_type, key_length,
568 : computed_key, &errstr) < 0)
569 : {
570 0 : elog(ERROR, "could not compute server key: %s", errstr);
571 : }
572 :
573 30 : if (prep_password)
574 30 : pfree(prep_password);
575 :
576 : /*
577 : * Compare the secret's Server Key with the one computed from the
578 : * user-supplied password.
579 : */
580 30 : return memcmp(computed_key, server_key, key_length) == 0;
581 : }
582 :
583 :
584 : /*
585 : * Parse and validate format of given SCRAM secret.
586 : *
587 : * On success, the iteration count, salt, stored key, and server key are
588 : * extracted from the secret, and returned to the caller. For 'stored_key'
589 : * and 'server_key', the caller must pass pre-allocated buffers of size
590 : * SCRAM_MAX_KEY_LEN. Salt is returned as a base64-encoded, null-terminated
591 : * string. The buffer for the salt is palloc'd by this function.
592 : *
593 : * Returns true if the SCRAM secret has been parsed, and false otherwise.
594 : */
595 : bool
596 508 : parse_scram_secret(const char *secret, int *iterations,
597 : pg_cryptohash_type *hash_type, int *key_length,
598 : char **salt, uint8 *stored_key, uint8 *server_key)
599 : {
600 : char *v;
601 : char *p;
602 : char *scheme_str;
603 : char *salt_str;
604 : char *iterations_str;
605 : char *storedkey_str;
606 : char *serverkey_str;
607 : int decoded_len;
608 : char *decoded_salt_buf;
609 : char *decoded_stored_buf;
610 : char *decoded_server_buf;
611 :
612 : /*
613 : * The secret is of form:
614 : *
615 : * SCRAM-SHA-256$<iterations>:<salt>$<storedkey>:<serverkey>
616 : */
617 508 : v = pstrdup(secret);
618 508 : if ((scheme_str = strtok(v, "$")) == NULL)
619 0 : goto invalid_secret;
620 508 : if ((iterations_str = strtok(NULL, ":")) == NULL)
621 200 : goto invalid_secret;
622 308 : if ((salt_str = strtok(NULL, "$")) == NULL)
623 12 : goto invalid_secret;
624 296 : if ((storedkey_str = strtok(NULL, ":")) == NULL)
625 0 : goto invalid_secret;
626 296 : if ((serverkey_str = strtok(NULL, "")) == NULL)
627 0 : goto invalid_secret;
628 :
629 : /* Parse the fields */
630 296 : if (strcmp(scheme_str, "SCRAM-SHA-256") != 0)
631 0 : goto invalid_secret;
632 296 : *hash_type = PG_SHA256;
633 296 : *key_length = SCRAM_SHA_256_KEY_LEN;
634 :
635 296 : errno = 0;
636 296 : *iterations = strtol(iterations_str, &p, 10);
637 296 : if (*p || errno != 0)
638 0 : goto invalid_secret;
639 :
640 : /*
641 : * Verify that the salt is in Base64-encoded format, by decoding it,
642 : * although we return the encoded version to the caller.
643 : */
644 296 : decoded_len = pg_b64_dec_len(strlen(salt_str));
645 296 : decoded_salt_buf = palloc(decoded_len);
646 296 : decoded_len = pg_b64_decode(salt_str, strlen(salt_str),
647 : decoded_salt_buf, decoded_len);
648 296 : if (decoded_len < 0)
649 0 : goto invalid_secret;
650 296 : *salt = pstrdup(salt_str);
651 :
652 : /*
653 : * Decode StoredKey and ServerKey.
654 : */
655 296 : decoded_len = pg_b64_dec_len(strlen(storedkey_str));
656 296 : decoded_stored_buf = palloc(decoded_len);
657 296 : decoded_len = pg_b64_decode(storedkey_str, strlen(storedkey_str),
658 : decoded_stored_buf, decoded_len);
659 296 : if (decoded_len != *key_length)
660 12 : goto invalid_secret;
661 284 : memcpy(stored_key, decoded_stored_buf, *key_length);
662 :
663 284 : decoded_len = pg_b64_dec_len(strlen(serverkey_str));
664 284 : decoded_server_buf = palloc(decoded_len);
665 284 : decoded_len = pg_b64_decode(serverkey_str, strlen(serverkey_str),
666 : decoded_server_buf, decoded_len);
667 284 : if (decoded_len != *key_length)
668 12 : goto invalid_secret;
669 272 : memcpy(server_key, decoded_server_buf, *key_length);
670 :
671 272 : return true;
672 :
673 236 : invalid_secret:
674 236 : *salt = NULL;
675 236 : return false;
676 : }
677 :
678 : /*
679 : * Generate plausible SCRAM secret parameters for mock authentication.
680 : *
681 : * In a normal authentication, these are extracted from the secret
682 : * stored in the server. This function generates values that look
683 : * realistic, for when there is no stored secret, using SCRAM-SHA-256.
684 : *
685 : * Like in parse_scram_secret(), for 'stored_key' and 'server_key', the
686 : * caller must pass pre-allocated buffers of size SCRAM_MAX_KEY_LEN, and
687 : * the buffer for the salt is palloc'd by this function.
688 : */
689 : static void
690 2 : mock_scram_secret(const char *username, pg_cryptohash_type *hash_type,
691 : int *iterations, int *key_length, char **salt,
692 : uint8 *stored_key, uint8 *server_key)
693 : {
694 : char *raw_salt;
695 : char *encoded_salt;
696 : int encoded_len;
697 :
698 : /* Enforce the use of SHA-256, which would be realistic enough */
699 2 : *hash_type = PG_SHA256;
700 2 : *key_length = SCRAM_SHA_256_KEY_LEN;
701 :
702 : /*
703 : * Generate deterministic salt.
704 : *
705 : * Note that we cannot reveal any information to an attacker here so the
706 : * error messages need to remain generic. This should never fail anyway
707 : * as the salt generated for mock authentication uses the cluster's nonce
708 : * value.
709 : */
710 2 : raw_salt = scram_mock_salt(username, *hash_type, *key_length);
711 2 : if (raw_salt == NULL)
712 0 : elog(ERROR, "could not encode salt");
713 :
714 2 : encoded_len = pg_b64_enc_len(SCRAM_DEFAULT_SALT_LEN);
715 : /* don't forget the zero-terminator */
716 2 : encoded_salt = (char *) palloc(encoded_len + 1);
717 2 : encoded_len = pg_b64_encode(raw_salt, SCRAM_DEFAULT_SALT_LEN, encoded_salt,
718 : encoded_len);
719 :
720 2 : if (encoded_len < 0)
721 0 : elog(ERROR, "could not encode salt");
722 2 : encoded_salt[encoded_len] = '\0';
723 :
724 2 : *salt = encoded_salt;
725 2 : *iterations = SCRAM_SHA_256_DEFAULT_ITERATIONS;
726 :
727 : /* StoredKey and ServerKey are not used in a doomed authentication */
728 2 : memset(stored_key, 0, SCRAM_MAX_KEY_LEN);
729 2 : memset(server_key, 0, SCRAM_MAX_KEY_LEN);
730 2 : }
731 :
732 : /*
733 : * Read the value in a given SCRAM exchange message for given attribute.
734 : */
735 : static char *
736 264 : read_attr_value(char **input, char attr)
737 : {
738 264 : char *begin = *input;
739 : char *end;
740 :
741 264 : if (*begin != attr)
742 0 : ereport(ERROR,
743 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
744 : errmsg("malformed SCRAM message"),
745 : errdetail("Expected attribute \"%c\" but found \"%s\".",
746 : attr, sanitize_char(*begin))));
747 264 : begin++;
748 :
749 264 : if (*begin != '=')
750 0 : ereport(ERROR,
751 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
752 : errmsg("malformed SCRAM message"),
753 : errdetail("Expected character \"=\" for attribute \"%c\".", attr)));
754 264 : begin++;
755 :
756 264 : end = begin;
757 5864 : while (*end && *end != ',')
758 5600 : end++;
759 :
760 264 : if (*end)
761 : {
762 200 : *end = '\0';
763 200 : *input = end + 1;
764 : }
765 : else
766 64 : *input = end;
767 :
768 264 : return begin;
769 : }
770 :
771 : static bool
772 64 : is_scram_printable(char *p)
773 : {
774 : /*------
775 : * Printable characters, as defined by SCRAM spec: (RFC 5802)
776 : *
777 : * printable = %x21-2B / %x2D-7E
778 : * ;; Printable ASCII except ",".
779 : * ;; Note that any "printable" is also
780 : * ;; a valid "value".
781 : *------
782 : */
783 1600 : for (; *p; p++)
784 : {
785 1536 : if (*p < 0x21 || *p > 0x7E || *p == 0x2C /* comma */ )
786 0 : return false;
787 : }
788 64 : return true;
789 : }
790 :
791 : /*
792 : * Convert an arbitrary byte to printable form. For error messages.
793 : *
794 : * If it's a printable ASCII character, print it as a single character.
795 : * otherwise, print it in hex.
796 : *
797 : * The returned pointer points to a static buffer.
798 : */
799 : static char *
800 0 : sanitize_char(char c)
801 : {
802 : static char buf[5];
803 :
804 0 : if (c >= 0x21 && c <= 0x7E)
805 0 : snprintf(buf, sizeof(buf), "'%c'", c);
806 : else
807 0 : snprintf(buf, sizeof(buf), "0x%02x", (unsigned char) c);
808 0 : return buf;
809 : }
810 :
811 : /*
812 : * Convert an arbitrary string to printable form, for error messages.
813 : *
814 : * Anything that's not a printable ASCII character is replaced with
815 : * '?', and the string is truncated at 30 characters.
816 : *
817 : * The returned pointer points to a static buffer.
818 : */
819 : static char *
820 0 : sanitize_str(const char *s)
821 : {
822 : static char buf[30 + 1];
823 : int i;
824 :
825 0 : for (i = 0; i < sizeof(buf) - 1; i++)
826 : {
827 0 : char c = s[i];
828 :
829 0 : if (c == '\0')
830 0 : break;
831 :
832 0 : if (c >= 0x21 && c <= 0x7E)
833 0 : buf[i] = c;
834 : else
835 0 : buf[i] = '?';
836 : }
837 0 : buf[i] = '\0';
838 0 : return buf;
839 : }
840 :
841 : /*
842 : * Read the next attribute and value in a SCRAM exchange message.
843 : *
844 : * The attribute character is set in *attr_p, the attribute value is the
845 : * return value.
846 : */
847 : static char *
848 64 : read_any_attr(char **input, char *attr_p)
849 : {
850 64 : char *begin = *input;
851 : char *end;
852 64 : char attr = *begin;
853 :
854 64 : if (attr == '\0')
855 0 : ereport(ERROR,
856 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
857 : errmsg("malformed SCRAM message"),
858 : errdetail("Attribute expected, but found end of string.")));
859 :
860 : /*------
861 : * attr-val = ALPHA "=" value
862 : * ;; Generic syntax of any attribute sent
863 : * ;; by server or client
864 : *------
865 : */
866 64 : if (!((attr >= 'A' && attr <= 'Z') ||
867 64 : (attr >= 'a' && attr <= 'z')))
868 0 : ereport(ERROR,
869 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
870 : errmsg("malformed SCRAM message"),
871 : errdetail("Attribute expected, but found invalid character \"%s\".",
872 : sanitize_char(attr))));
873 64 : if (attr_p)
874 64 : *attr_p = attr;
875 64 : begin++;
876 :
877 64 : if (*begin != '=')
878 0 : ereport(ERROR,
879 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
880 : errmsg("malformed SCRAM message"),
881 : errdetail("Expected character \"=\" for attribute \"%c\".", attr)));
882 64 : begin++;
883 :
884 64 : end = begin;
885 2880 : while (*end && *end != ',')
886 2816 : end++;
887 :
888 64 : if (*end)
889 : {
890 0 : *end = '\0';
891 0 : *input = end + 1;
892 : }
893 : else
894 64 : *input = end;
895 :
896 64 : return begin;
897 : }
898 :
899 : /*
900 : * Read and parse the first message from client in the context of a SCRAM
901 : * authentication exchange message.
902 : *
903 : * At this stage, any errors will be reported directly with ereport(ERROR).
904 : */
905 : static void
906 64 : read_client_first_message(scram_state *state, const char *input)
907 : {
908 64 : char *p = pstrdup(input);
909 : char *channel_binding_type;
910 :
911 :
912 : /*------
913 : * The syntax for the client-first-message is: (RFC 5802)
914 : *
915 : * saslname = 1*(value-safe-char / "=2C" / "=3D")
916 : * ;; Conforms to <value>.
917 : *
918 : * authzid = "a=" saslname
919 : * ;; Protocol specific.
920 : *
921 : * cb-name = 1*(ALPHA / DIGIT / "." / "-")
922 : * ;; See RFC 5056, Section 7.
923 : * ;; E.g., "tls-server-end-point" or
924 : * ;; "tls-unique".
925 : *
926 : * gs2-cbind-flag = ("p=" cb-name) / "n" / "y"
927 : * ;; "n" -> client doesn't support channel binding.
928 : * ;; "y" -> client does support channel binding
929 : * ;; but thinks the server does not.
930 : * ;; "p" -> client requires channel binding.
931 : * ;; The selected channel binding follows "p=".
932 : *
933 : * gs2-header = gs2-cbind-flag "," [ authzid ] ","
934 : * ;; GS2 header for SCRAM
935 : * ;; (the actual GS2 header includes an optional
936 : * ;; flag to indicate that the GSS mechanism is not
937 : * ;; "standard", but since SCRAM is "standard", we
938 : * ;; don't include that flag).
939 : *
940 : * username = "n=" saslname
941 : * ;; Usernames are prepared using SASLprep.
942 : *
943 : * reserved-mext = "m=" 1*(value-char)
944 : * ;; Reserved for signaling mandatory extensions.
945 : * ;; The exact syntax will be defined in
946 : * ;; the future.
947 : *
948 : * nonce = "r=" c-nonce [s-nonce]
949 : * ;; Second part provided by server.
950 : *
951 : * c-nonce = printable
952 : *
953 : * client-first-message-bare =
954 : * [reserved-mext ","]
955 : * username "," nonce ["," extensions]
956 : *
957 : * client-first-message =
958 : * gs2-header client-first-message-bare
959 : *
960 : * For example:
961 : * n,,n=user,r=fyko+d2lbbFgONRv9qkxdawL
962 : *
963 : * The "n,," in the beginning means that the client doesn't support
964 : * channel binding, and no authzid is given. "n=user" is the username.
965 : * However, in PostgreSQL the username is sent in the startup packet, and
966 : * the username in the SCRAM exchange is ignored. libpq always sends it
967 : * as an empty string. The last part, "r=fyko+d2lbbFgONRv9qkxdawL" is
968 : * the client nonce.
969 : *------
970 : */
971 :
972 : /*
973 : * Read gs2-cbind-flag. (For details see also RFC 5802 Section 6 "Channel
974 : * Binding".)
975 : */
976 64 : state->cbind_flag = *p;
977 64 : switch (*p)
978 : {
979 56 : case 'n':
980 :
981 : /*
982 : * The client does not support channel binding or has simply
983 : * decided to not use it. In that case just let it go.
984 : */
985 56 : if (state->channel_binding_in_use)
986 0 : ereport(ERROR,
987 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
988 : errmsg("malformed SCRAM message"),
989 : errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
990 :
991 56 : p++;
992 56 : if (*p != ',')
993 0 : ereport(ERROR,
994 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
995 : errmsg("malformed SCRAM message"),
996 : errdetail("Comma expected, but found character \"%s\".",
997 : sanitize_char(*p))));
998 56 : p++;
999 56 : break;
1000 0 : case 'y':
1001 :
1002 : /*
1003 : * The client supports channel binding and thinks that the server
1004 : * does not. In this case, the server must fail authentication if
1005 : * it supports channel binding.
1006 : */
1007 0 : if (state->channel_binding_in_use)
1008 0 : ereport(ERROR,
1009 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1010 : errmsg("malformed SCRAM message"),
1011 : errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
1012 :
1013 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
1014 0 : if (state->port->ssl_in_use)
1015 0 : ereport(ERROR,
1016 : (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
1017 : errmsg("SCRAM channel binding negotiation error"),
1018 : errdetail("The client supports SCRAM channel binding but thinks the server does not. "
1019 : "However, this server does support channel binding.")));
1020 : #endif
1021 0 : p++;
1022 0 : if (*p != ',')
1023 0 : ereport(ERROR,
1024 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1025 : errmsg("malformed SCRAM message"),
1026 : errdetail("Comma expected, but found character \"%s\".",
1027 : sanitize_char(*p))));
1028 0 : p++;
1029 0 : break;
1030 8 : case 'p':
1031 :
1032 : /*
1033 : * The client requires channel binding. Channel binding type
1034 : * follows, e.g., "p=tls-server-end-point".
1035 : */
1036 8 : if (!state->channel_binding_in_use)
1037 0 : ereport(ERROR,
1038 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1039 : errmsg("malformed SCRAM message"),
1040 : errdetail("The client selected SCRAM-SHA-256 without channel binding, but the SCRAM message includes channel binding data.")));
1041 :
1042 8 : channel_binding_type = read_attr_value(&p, 'p');
1043 :
1044 : /*
1045 : * The only channel binding type we support is
1046 : * tls-server-end-point.
1047 : */
1048 8 : if (strcmp(channel_binding_type, "tls-server-end-point") != 0)
1049 0 : ereport(ERROR,
1050 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1051 : errmsg("unsupported SCRAM channel-binding type \"%s\"",
1052 : sanitize_str(channel_binding_type))));
1053 8 : break;
1054 0 : default:
1055 0 : ereport(ERROR,
1056 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1057 : errmsg("malformed SCRAM message"),
1058 : errdetail("Unexpected channel-binding flag \"%s\".",
1059 : sanitize_char(*p))));
1060 : }
1061 :
1062 : /*
1063 : * Forbid optional authzid (authorization identity). We don't support it.
1064 : */
1065 64 : if (*p == 'a')
1066 0 : ereport(ERROR,
1067 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1068 : errmsg("client uses authorization identity, but it is not supported")));
1069 64 : if (*p != ',')
1070 0 : ereport(ERROR,
1071 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1072 : errmsg("malformed SCRAM message"),
1073 : errdetail("Unexpected attribute \"%s\" in client-first-message.",
1074 : sanitize_char(*p))));
1075 64 : p++;
1076 :
1077 64 : state->client_first_message_bare = pstrdup(p);
1078 :
1079 : /*
1080 : * Any mandatory extensions would go here. We don't support any.
1081 : *
1082 : * RFC 5802 specifies error code "e=extensions-not-supported" for this,
1083 : * but it can only be sent in the server-final message. We prefer to fail
1084 : * immediately (which the RFC also allows).
1085 : */
1086 64 : if (*p == 'm')
1087 0 : ereport(ERROR,
1088 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1089 : errmsg("client requires an unsupported SCRAM extension")));
1090 :
1091 : /*
1092 : * Read username. Note: this is ignored. We use the username from the
1093 : * startup message instead, still it is kept around if provided as it
1094 : * proves to be useful for debugging purposes.
1095 : */
1096 64 : state->client_username = read_attr_value(&p, 'n');
1097 :
1098 : /* read nonce and check that it is made of only printable characters */
1099 64 : state->client_nonce = read_attr_value(&p, 'r');
1100 64 : if (!is_scram_printable(state->client_nonce))
1101 0 : ereport(ERROR,
1102 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1103 : errmsg("non-printable characters in SCRAM nonce")));
1104 :
1105 : /*
1106 : * There can be any number of optional extensions after this. We don't
1107 : * support any extensions, so ignore them.
1108 : */
1109 64 : while (*p != '\0')
1110 0 : read_any_attr(&p, NULL);
1111 :
1112 : /* success! */
1113 64 : }
1114 :
1115 : /*
1116 : * Verify the final nonce contained in the last message received from
1117 : * client in an exchange.
1118 : */
1119 : static bool
1120 64 : verify_final_nonce(scram_state *state)
1121 : {
1122 64 : int client_nonce_len = strlen(state->client_nonce);
1123 64 : int server_nonce_len = strlen(state->server_nonce);
1124 64 : int final_nonce_len = strlen(state->client_final_nonce);
1125 :
1126 64 : if (final_nonce_len != client_nonce_len + server_nonce_len)
1127 0 : return false;
1128 64 : if (memcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
1129 0 : return false;
1130 64 : if (memcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
1131 0 : return false;
1132 :
1133 64 : return true;
1134 : }
1135 :
1136 : /*
1137 : * Verify the client proof contained in the last message received from
1138 : * client in an exchange. Returns true if the verification is a success,
1139 : * or false for a failure.
1140 : */
1141 : static bool
1142 64 : verify_client_proof(scram_state *state)
1143 : {
1144 : uint8 ClientSignature[SCRAM_MAX_KEY_LEN];
1145 : uint8 ClientKey[SCRAM_MAX_KEY_LEN];
1146 : uint8 client_StoredKey[SCRAM_MAX_KEY_LEN];
1147 64 : pg_hmac_ctx *ctx = pg_hmac_create(state->hash_type);
1148 : int i;
1149 64 : const char *errstr = NULL;
1150 :
1151 : /*
1152 : * Calculate ClientSignature. Note that we don't log directly a failure
1153 : * here even when processing the calculations as this could involve a mock
1154 : * authentication.
1155 : */
1156 128 : if (pg_hmac_init(ctx, state->StoredKey, state->key_length) < 0 ||
1157 64 : pg_hmac_update(ctx,
1158 64 : (uint8 *) state->client_first_message_bare,
1159 128 : strlen(state->client_first_message_bare)) < 0 ||
1160 128 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1161 64 : pg_hmac_update(ctx,
1162 64 : (uint8 *) state->server_first_message,
1163 128 : strlen(state->server_first_message)) < 0 ||
1164 128 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1165 64 : pg_hmac_update(ctx,
1166 64 : (uint8 *) state->client_final_message_without_proof,
1167 128 : strlen(state->client_final_message_without_proof)) < 0 ||
1168 64 : pg_hmac_final(ctx, ClientSignature, state->key_length) < 0)
1169 : {
1170 0 : elog(ERROR, "could not calculate client signature: %s",
1171 : pg_hmac_error(ctx));
1172 : }
1173 :
1174 64 : pg_hmac_free(ctx);
1175 :
1176 : /* Extract the ClientKey that the client calculated from the proof */
1177 2112 : for (i = 0; i < state->key_length; i++)
1178 2048 : ClientKey[i] = state->ClientProof[i] ^ ClientSignature[i];
1179 :
1180 : /* Hash it one more time, and compare with StoredKey */
1181 64 : if (scram_H(ClientKey, state->hash_type, state->key_length,
1182 : client_StoredKey, &errstr) < 0)
1183 0 : elog(ERROR, "could not hash stored key: %s", errstr);
1184 :
1185 64 : if (memcmp(client_StoredKey, state->StoredKey, state->key_length) != 0)
1186 10 : return false;
1187 :
1188 54 : return true;
1189 : }
1190 :
1191 : /*
1192 : * Build the first server-side message sent to the client in a SCRAM
1193 : * communication exchange.
1194 : */
1195 : static char *
1196 64 : build_server_first_message(scram_state *state)
1197 : {
1198 : /*------
1199 : * The syntax for the server-first-message is: (RFC 5802)
1200 : *
1201 : * server-first-message =
1202 : * [reserved-mext ","] nonce "," salt ","
1203 : * iteration-count ["," extensions]
1204 : *
1205 : * nonce = "r=" c-nonce [s-nonce]
1206 : * ;; Second part provided by server.
1207 : *
1208 : * c-nonce = printable
1209 : *
1210 : * s-nonce = printable
1211 : *
1212 : * salt = "s=" base64
1213 : *
1214 : * iteration-count = "i=" posit-number
1215 : * ;; A positive number.
1216 : *
1217 : * Example:
1218 : *
1219 : * r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,s=QSXCR+Q6sek8bf92,i=4096
1220 : *------
1221 : */
1222 :
1223 : /*
1224 : * Per the spec, the nonce may consist of any printable ASCII characters.
1225 : * For convenience, however, we don't use the whole range available,
1226 : * rather, we generate some random bytes, and base64 encode them.
1227 : */
1228 : char raw_nonce[SCRAM_RAW_NONCE_LEN];
1229 : int encoded_len;
1230 :
1231 64 : if (!pg_strong_random(raw_nonce, SCRAM_RAW_NONCE_LEN))
1232 0 : ereport(ERROR,
1233 : (errcode(ERRCODE_INTERNAL_ERROR),
1234 : errmsg("could not generate random nonce")));
1235 :
1236 64 : encoded_len = pg_b64_enc_len(SCRAM_RAW_NONCE_LEN);
1237 : /* don't forget the zero-terminator */
1238 64 : state->server_nonce = palloc(encoded_len + 1);
1239 64 : encoded_len = pg_b64_encode(raw_nonce, SCRAM_RAW_NONCE_LEN,
1240 : state->server_nonce, encoded_len);
1241 64 : if (encoded_len < 0)
1242 0 : ereport(ERROR,
1243 : (errcode(ERRCODE_INTERNAL_ERROR),
1244 : errmsg("could not encode random nonce")));
1245 64 : state->server_nonce[encoded_len] = '\0';
1246 :
1247 64 : state->server_first_message =
1248 64 : psprintf("r=%s%s,s=%s,i=%d",
1249 : state->client_nonce, state->server_nonce,
1250 : state->salt, state->iterations);
1251 :
1252 64 : return pstrdup(state->server_first_message);
1253 : }
1254 :
1255 :
1256 : /*
1257 : * Read and parse the final message received from client.
1258 : */
1259 : static void
1260 64 : read_client_final_message(scram_state *state, const char *input)
1261 : {
1262 : char attr;
1263 : char *channel_binding;
1264 : char *value;
1265 : char *begin,
1266 : *proof;
1267 : char *p;
1268 : char *client_proof;
1269 : int client_proof_len;
1270 :
1271 64 : begin = p = pstrdup(input);
1272 :
1273 : /*------
1274 : * The syntax for the server-first-message is: (RFC 5802)
1275 : *
1276 : * gs2-header = gs2-cbind-flag "," [ authzid ] ","
1277 : * ;; GS2 header for SCRAM
1278 : * ;; (the actual GS2 header includes an optional
1279 : * ;; flag to indicate that the GSS mechanism is not
1280 : * ;; "standard", but since SCRAM is "standard", we
1281 : * ;; don't include that flag).
1282 : *
1283 : * cbind-input = gs2-header [ cbind-data ]
1284 : * ;; cbind-data MUST be present for
1285 : * ;; gs2-cbind-flag of "p" and MUST be absent
1286 : * ;; for "y" or "n".
1287 : *
1288 : * channel-binding = "c=" base64
1289 : * ;; base64 encoding of cbind-input.
1290 : *
1291 : * proof = "p=" base64
1292 : *
1293 : * client-final-message-without-proof =
1294 : * channel-binding "," nonce [","
1295 : * extensions]
1296 : *
1297 : * client-final-message =
1298 : * client-final-message-without-proof "," proof
1299 : *------
1300 : */
1301 :
1302 : /*
1303 : * Read channel binding. This repeats the channel-binding flags and is
1304 : * then followed by the actual binding data depending on the type.
1305 : */
1306 64 : channel_binding = read_attr_value(&p, 'c');
1307 64 : if (state->channel_binding_in_use)
1308 : {
1309 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
1310 8 : const char *cbind_data = NULL;
1311 8 : size_t cbind_data_len = 0;
1312 : size_t cbind_header_len;
1313 : char *cbind_input;
1314 : size_t cbind_input_len;
1315 : char *b64_message;
1316 : int b64_message_len;
1317 :
1318 : Assert(state->cbind_flag == 'p');
1319 :
1320 : /* Fetch hash data of server's SSL certificate */
1321 8 : cbind_data = be_tls_get_certificate_hash(state->port,
1322 : &cbind_data_len);
1323 :
1324 : /* should not happen */
1325 8 : if (cbind_data == NULL || cbind_data_len == 0)
1326 0 : elog(ERROR, "could not get server certificate hash");
1327 :
1328 8 : cbind_header_len = strlen("p=tls-server-end-point,,"); /* p=type,, */
1329 8 : cbind_input_len = cbind_header_len + cbind_data_len;
1330 8 : cbind_input = palloc(cbind_input_len);
1331 8 : snprintf(cbind_input, cbind_input_len, "p=tls-server-end-point,,");
1332 8 : memcpy(cbind_input + cbind_header_len, cbind_data, cbind_data_len);
1333 :
1334 8 : b64_message_len = pg_b64_enc_len(cbind_input_len);
1335 : /* don't forget the zero-terminator */
1336 8 : b64_message = palloc(b64_message_len + 1);
1337 8 : b64_message_len = pg_b64_encode(cbind_input, cbind_input_len,
1338 : b64_message, b64_message_len);
1339 8 : if (b64_message_len < 0)
1340 0 : elog(ERROR, "could not encode channel binding data");
1341 8 : b64_message[b64_message_len] = '\0';
1342 :
1343 : /*
1344 : * Compare the value sent by the client with the value expected by the
1345 : * server.
1346 : */
1347 8 : if (strcmp(channel_binding, b64_message) != 0)
1348 0 : ereport(ERROR,
1349 : (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
1350 : errmsg("SCRAM channel binding check failed")));
1351 : #else
1352 : /* shouldn't happen, because we checked this earlier already */
1353 : elog(ERROR, "channel binding not supported by this build");
1354 : #endif
1355 : }
1356 : else
1357 : {
1358 : /*
1359 : * If we are not using channel binding, the binding data is expected
1360 : * to always be "biws", which is "n,," base64-encoded, or "eSws",
1361 : * which is "y,,". We also have to check whether the flag is the same
1362 : * one that the client originally sent.
1363 : */
1364 56 : if (!(strcmp(channel_binding, "biws") == 0 && state->cbind_flag == 'n') &&
1365 0 : !(strcmp(channel_binding, "eSws") == 0 && state->cbind_flag == 'y'))
1366 0 : ereport(ERROR,
1367 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1368 : errmsg("unexpected SCRAM channel-binding attribute in client-final-message")));
1369 : }
1370 :
1371 64 : state->client_final_nonce = read_attr_value(&p, 'r');
1372 :
1373 : /* ignore optional extensions, read until we find "p" attribute */
1374 : do
1375 : {
1376 64 : proof = p - 1;
1377 64 : value = read_any_attr(&p, &attr);
1378 64 : } while (attr != 'p');
1379 :
1380 64 : client_proof_len = pg_b64_dec_len(strlen(value));
1381 64 : client_proof = palloc(client_proof_len);
1382 64 : if (pg_b64_decode(value, strlen(value), client_proof,
1383 64 : client_proof_len) != state->key_length)
1384 0 : ereport(ERROR,
1385 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1386 : errmsg("malformed SCRAM message"),
1387 : errdetail("Malformed proof in client-final-message.")));
1388 64 : memcpy(state->ClientProof, client_proof, state->key_length);
1389 64 : pfree(client_proof);
1390 :
1391 64 : if (*p != '\0')
1392 0 : ereport(ERROR,
1393 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1394 : errmsg("malformed SCRAM message"),
1395 : errdetail("Garbage found at the end of client-final-message.")));
1396 :
1397 64 : state->client_final_message_without_proof = palloc(proof - begin + 1);
1398 64 : memcpy(state->client_final_message_without_proof, input, proof - begin);
1399 64 : state->client_final_message_without_proof[proof - begin] = '\0';
1400 64 : }
1401 :
1402 : /*
1403 : * Build the final server-side message of an exchange.
1404 : */
1405 : static char *
1406 54 : build_server_final_message(scram_state *state)
1407 : {
1408 : uint8 ServerSignature[SCRAM_MAX_KEY_LEN];
1409 : char *server_signature_base64;
1410 : int siglen;
1411 54 : pg_hmac_ctx *ctx = pg_hmac_create(state->hash_type);
1412 :
1413 : /* calculate ServerSignature */
1414 108 : if (pg_hmac_init(ctx, state->ServerKey, state->key_length) < 0 ||
1415 54 : pg_hmac_update(ctx,
1416 54 : (uint8 *) state->client_first_message_bare,
1417 108 : strlen(state->client_first_message_bare)) < 0 ||
1418 108 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1419 54 : pg_hmac_update(ctx,
1420 54 : (uint8 *) state->server_first_message,
1421 108 : strlen(state->server_first_message)) < 0 ||
1422 108 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1423 54 : pg_hmac_update(ctx,
1424 54 : (uint8 *) state->client_final_message_without_proof,
1425 108 : strlen(state->client_final_message_without_proof)) < 0 ||
1426 54 : pg_hmac_final(ctx, ServerSignature, state->key_length) < 0)
1427 : {
1428 0 : elog(ERROR, "could not calculate server signature: %s",
1429 : pg_hmac_error(ctx));
1430 : }
1431 :
1432 54 : pg_hmac_free(ctx);
1433 :
1434 54 : siglen = pg_b64_enc_len(state->key_length);
1435 : /* don't forget the zero-terminator */
1436 54 : server_signature_base64 = palloc(siglen + 1);
1437 54 : siglen = pg_b64_encode((const char *) ServerSignature,
1438 : state->key_length, server_signature_base64,
1439 : siglen);
1440 54 : if (siglen < 0)
1441 0 : elog(ERROR, "could not encode server signature");
1442 54 : server_signature_base64[siglen] = '\0';
1443 :
1444 : /*------
1445 : * The syntax for the server-final-message is: (RFC 5802)
1446 : *
1447 : * verifier = "v=" base64
1448 : * ;; base-64 encoded ServerSignature.
1449 : *
1450 : * server-final-message = (server-error / verifier)
1451 : * ["," extensions]
1452 : *
1453 : *------
1454 : */
1455 54 : return psprintf("v=%s", server_signature_base64);
1456 : }
1457 :
1458 :
1459 : /*
1460 : * Deterministically generate salt for mock authentication, using a SHA256
1461 : * hash based on the username and a cluster-level secret key. Returns a
1462 : * pointer to a static buffer of size SCRAM_DEFAULT_SALT_LEN, or NULL.
1463 : */
1464 : static char *
1465 2 : scram_mock_salt(const char *username, pg_cryptohash_type hash_type,
1466 : int key_length)
1467 : {
1468 : pg_cryptohash_ctx *ctx;
1469 : static uint8 sha_digest[SCRAM_MAX_KEY_LEN];
1470 2 : char *mock_auth_nonce = GetMockAuthenticationNonce();
1471 :
1472 : /*
1473 : * Generate salt using a SHA256 hash of the username and the cluster's
1474 : * mock authentication nonce. (This works as long as the salt length is
1475 : * not larger than the SHA256 digest length. If the salt is smaller, the
1476 : * caller will just ignore the extra data.)
1477 : */
1478 : StaticAssertDecl(PG_SHA256_DIGEST_LENGTH >= SCRAM_DEFAULT_SALT_LEN,
1479 : "salt length greater than SHA256 digest length");
1480 :
1481 : /*
1482 : * This may be worth refreshing if support for more hash methods is\
1483 : * added.
1484 : */
1485 : Assert(hash_type == PG_SHA256);
1486 :
1487 2 : ctx = pg_cryptohash_create(hash_type);
1488 4 : if (pg_cryptohash_init(ctx) < 0 ||
1489 4 : pg_cryptohash_update(ctx, (uint8 *) username, strlen(username)) < 0 ||
1490 4 : pg_cryptohash_update(ctx, (uint8 *) mock_auth_nonce, MOCK_AUTH_NONCE_LEN) < 0 ||
1491 2 : pg_cryptohash_final(ctx, sha_digest, key_length) < 0)
1492 : {
1493 0 : pg_cryptohash_free(ctx);
1494 0 : return NULL;
1495 : }
1496 2 : pg_cryptohash_free(ctx);
1497 :
1498 2 : return (char *) sha_digest;
1499 : }
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